Run on the dyno, the FR500-inducted...
Run on the dyno, the FR500-inducted 4.6L made 435 hp at 6,100 rpm and a peak of 483 hp at 7,500 rpm.
Originally introduced in the Mustang in 1996, the Four-Valve modular motor recently gained a new lease on life when Ford introduced the latest and greatest 5.0L version. With the new Mustang sporting a 5.0L and the Shelby offering the supercharged 5.8L, you have to ask—where does that leave the old 4.6L?
Actually, the 4.6L Cobra motor is alive and well, for good reason. Though no aftermarket heads have become available, the factory stuff can be made to flow pretty well. With the proper porting, big cams, and a ported intake, you have the makings for one healthy beast—add cubes, like we did with our recent DOHC build, and you can crack 500 hp quite easily. Back that up with nitrous or boost and you're talking about really serious power.
One need only look at Accufab's John Mihovetz to see just how far you can take a 4.6L. With twin-turbo mod motors exceeding 2,000 hp, the 4.6L can still hold its own with the very best performance motors. And to illustrate what is possible on a normally aspirated 4.6L Cobra motor, we decided to subject one to a series of bolt-ons.
Probe Racing supplied a set...
Probe Racing supplied a set of flat-top pistons to duplicate the factory slugs. The pistons were used with a factory Cobra (steel) crank and forged rods. Note also the Fel Pro MLS gaskets and ARP head studs.
The idea was to first test a stock motor and then add performance components to illustrate how well the Cobra responded. The quad-cam arrangement on the 4.6L meant this would be best achieved on an engine dyno, though the head, cam, and intake swap could be accomplished in the car as well.
While a stock NA 4.6L Cobra motor would suffice, we already had a 4.6L test mule courtesy of Sean Hyland Motorports. The motor had seen plenty of abuse, having previously been subjected to all manners of normally aspirated and boosted modifications. Combine that with extended periods of inactive duty, and we decided the motor deserved at least a light hone and fresh set of rings.
L&R brought the short-block back to life, as well as sourcing us a set of stock Four-Valve heads to serve as our baseline. We already had stock cams from a previous test, so after the hone and new rings, the motor was reassembled using Fel Pro MLS head gaskets and ARP head studs. Odds are that this mod motor will eventually see boost, so the head gaskets and ARP hardware was money well spent.
The stock heads came off a low-mileage '01 Cobra and required only a clean-up before installation. Add in the stock intake and exhaust manifolds, and toss on a Meziere electric water pump, and we were in business.
1. The stock Cobra heads...
1. The stock Cobra heads were just freshened up and installed on the awaiting short-block.
Run with a FAST XFI, it produced 336 hp and 332 lb-ft of torque. Often considered a high-rpm motor, the Cobra produced peak power at just 6,000 rpm, while peak torque came at 4,900 rpm.
Having established a baseline, off came the stock heads, cams, and intake to make room for our upgrades. First on the list was a set of ported stock heads from Sean Hyland. In addition to full porting on the intake and exhaust, the heads were also treated to slightly larger valves and a valvespring upgrade that provided sufficient coil-bind clearance for the Comp cams we had planned. The spring upgrade also allowed the motor to rev safely to 7,500 rpm. The ported heads were combined with Comp XE262AH cams. The dual-pattern XE262AH cams offered 226 degrees of intake duration, 222 degrees of exhaust duration, and a 114-degree lobe separation angle to go along with the 0.425 lift (both intake and exhaust).
2. Both the stock and SHM...
2. Both the stock and SHM heads were treated to a set of Comp valvesprings. The spring upgrades allowed us to run these stock heads with aftermarket cams in the future.
3. All testing was run with...
3. All testing was run with the FAST XFI engine management system. The FAST made short work of tuning each new combination to (safely) maximize power production.
4. The stock Four-Valve was...
4. The stock Four-Valve was run with factory exhaust manifold, but we swapped them out in favor of Hooker headers on the modified Cobra motor.
5. Run in stock configuration,...
5. Run in stock configuration, the Four-Valve Cobra motor produced 336 hp and 332 lb-ft of torque.
6. First on our list of upgrades...
6. First on our list of upgrades was a set of ported heads from SHM. Though the stock Four-Valve heads flowed well, additional porting can unearth plenty of power.
7. The intake and exhaust...
7. The intake and exhaust ports were given the full treatment. Care must be taken not to port right through to a water jacket, but proper blending and bowl work can yield large dividends.
8. Our ported heads also...
8. Our ported heads also featured oversize valves to improve flow. At some point, the valves themselves become the choke point in terms of flow.
9. Working with the high-flow...
9. Working with the high-flow heads was a quartet of Comp cams. The XE262AH cams offered 0.425 lift (both intake and exhaust), a 226/222-degree duration split, and a 114-degree lobe separation.
10. The factory Cobra intake...
10. The factory Cobra intake was also the recipient of minor porting, though no change was made to the runner length.